Alarm-radio system



Ma 3, 1966 R. L; WEBER 3,249,874

ALARM-RADI O SYS TEM 5 Sheets-Sheet 1 Filed Aug. 6, 1962 ROGER L. WEBER INVENTOR.

v BY A y 3, 1966 R. LWEBER 3,249,874

ALARM-RADIO SYSTEM Filed Aug. 6 1962 5 Sheets-Sheet 2 FIG.3

ROGER L. WEBER INVENTOR.

United States Patent 3,249,874 ALARM-RADIO SYSTEM Roger L. Weber, Arlington, Tex., assignor, by mesne assiguments, to Cadre Industries Corp., Endicott, N .Y., a corporation of New York Filed Aug. 6, 1962, Ser. No. 215,111

Claims. (Cl. 325-390) This invention relates to an alarm-radio system and more particularly to a system for facilitating a change of function in a radio receiver from alarm stand-by to broadcast reception.

The effectiveness of an alarm transmitted for general population reception is dependent upon the general availability of receivers operated in a stand-by condition. In alarm proposals such as Conelrad and the like, special signal information is to be broadcast at selected radio frequencies. In any case, the broadcast of an alarm which results in effective widespread dissemination of information to the public is possibleonly if radio reception is widely maintained at all times. Further, in times of emergency it may be necessary to provide for communication over substantial periods during which normal power sources will not be operative;

The present invention is directed toward a battery powered alarm-radio which is operable on a continuous basis in a stand-by alarm condition and which may readily be changed from a stand-by alarm condition to a condi-' tion for reception of broadcast information.

More particularly in accordance with the present invention, there is provided a receiver which includes an alarm. Means are provided in the receiver for applying power to the alarm when the receiver is in stand-by condition. A switch means is provided in the receiver which upon actuation changes from alarm to communication operation.

More specifically, there is provided a radio alarm system which includes an RF. section and an audio section for the production of a signal at audio frequencies representative of modulation on a received R.F. carrier and for producing an audio output. A normally quiescent alarm unit is provided in the system which is adapted to be energized upon application thereto for at least a delay interval of a signal of a predetermined frequency. The receiver includes a power source therein which is in the form of a chargeable battery which normally receives a trickle charge current from the primary power source while powering the receiver-alarm unit. Selectively operable means are then provided for connecting said alarm unit to the audio section for stand-by alarm operation operable following reception of a signal at said frequency for at least the delay interval and for switching to conventional reception.

For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description 27 to the cathode of the detector 17a.

taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic diagram of one embodiment of the invention;

FIGURE 2 illustrates a modification of the invention in which two units areemployed;

FIGURE 3 is an isometric view, partly in section, showing one embodiment of the invention; and I FIGURE 4 is a block diagram of the embodiment of FIGURE 1.

Referring now to FIGURE 1, there is illustrated in schematic diagram form a radio receiver and alarm system. While the invention may be operable for AM, FM, or shortwave or other bands in the radio-frequency spectrum, the example of FIGURE 1 is a transistorized 3,249,874 Patented May 3, 1966 AM receiver, battery-powered and operable either in a Zt and-by alarm condition or in a broadcast reception conition.

More particularly, a receiving antenna 10 is provided at the input of the signal channel in which a mixeroscillater stage 11 includes a transistor 11a. Tuning capacitors 10a and 11b are mechanically coupled as by link 110 so that the local oscillator including transistor 11a may be made to track the signal to which the circuit including the antenna 10 is tuned.

An I.F. signal is then transmitted by way of the IF. transformer 12 to the first I.F. amplifier 13. The signal is then transmitted by way of LP. transformer 14 to the second I.F. stage 15.

A third I.F. transformer 16 is connected at its output to a demodulator 17, including diode 17a, which provides an audio output signal which is developed across a condenser 170. A resistor 17b is connected between diode 17a and a volume control 17e. A condenser 17d is connected across the control 172.

The variable tap on the volume control 17e is connected to terminal 18 of a first section 19a of a multisection switch 19. With the selector arm of switch 19a connected to terminal 18, the signal detected in the demodulator 17 is applied to an audio-amplifying channel which includes a driver transistor 21 and an output amplifier 22. The output of stage 22 is applied by way of switch sections 19b and 190 to a speaker 25. The switch sections 19b and 190 are second and third section, respectively, of the multisection switch 19 and are coupled to section 19a by the linkage (shown dotted). Both the RF. section and audio section of the receiver are powered from a battery 30, the negative terminal of which is connected to bus 31 by way of the on-oif switch 28 and the relay 99. The positive terminal of battery 30 is connected to a ground reference terminal or bus 32.

For broadcast reception the volume control 17e provides adjustment to the desired audio output level at speaker 25. With the system in a stand-by alarm condition, the second terminal 20 of switch section 19a is connected for maximum gain through resistors 17b and By this means, the maximum signal output is applied by way of section 19a to the audio amplifier.

In the stand-by condition it will be noted that the switches 19b and 19c disconnect the amplifier 22 from the speaker 25 and connect it to a resonant reed relay coil 60. Reed contact 62 is connected to ground. The vibrating reed 63 actuated by and upon energization of coil 60 is connected by way of resistor 64 and the RC network 65 to the bus 31.

The battery 30 is trickle-charged from a power supply circuit including a plug 70 which may be connected to a power line as by a convenience outlet to apply alternating current to the power supply transformer 71. The secondary winding of the transformer 71 is connected at its center terminal to ground and at its extermities to rectifiers 72 and 73. The anodes of the rectifiers 72 and 73 are connected together and to a condenser 74. A voltage regulator 75 is connected at its output to the negative terminal of batteryv 30 to maintain atrickle charge on the battery 30. It will be noted that power is applied to the bus 31 from battery 30 only when the switch 28 is closed.

The RC circuit 65 is connected by way of resistor to the base of a transistor 81 whose emitter is connected to thebus 31. The collector of transistor 81 and the base of transistor 83 are interconnected. The emitter of transistor 83 is connected by way of diode 84 to the bus .31 and, by way of resistance 85, to the ground bus 32.

Condenser 87 connects the collector of transistor 83 to the ground bus 32. Series resistances 88 and 89 parallel condenser 87 with the juncture between resistances 88 and 89 being connected to the base of transistor 90, and, by wayof condenser 91, to the bus 31. The collector of transistor 90 is connected to the bus 31. The emitter is connected by way of resistance 92 to the bus 32 and to the emitter of a transistor 93. The base of transistor 93 is connected by way of resistance 94 to the bus 32 and by way of variable resistance 95 and resistance 96 to the bus 31. The collector of transistor 93 is connected by way of resistance 97 to thebus 31 and also to the base of transistor 98.

The transistor 98 is connected in series with a relay coil 99. More particularly, the emitter of transistor 98 is connected to the bus by way of resistor 96 and the collector is connected to one terminal of the coil 99. The other terminal of the latter coil is connected to the bus 32. The relay coil 99 serves to actuate the switch arm 99a which is connected to the switch 28. Terminal 9% is connected to bus 31 and the other terminal 99c is connected by way of resistance 100 to the collector of transistor 98 and to a buzzer alarm unit 101 which includes a vibrating contact 102 and an energizing coil 103.

In order to provide desired operation, the resonant reed 63 is sharply tuned, vibrating only when an alternating current signal of sufiicient amplitude and at the exact frequency to which the reed is tuned is applied across the terminals of coil 60. When the reed 63 vibrates, it makes intermittent contact to close the circuit from ground terminal 62 to the RC circuit 65. The intermittent contact thus made serves to apply intermittent pulses to the circuit 65 wherein they are integrated. The system response is thus keyed as to frequency and produces a DC. voltage which is applied through resistance 80 to the base of transistor 81. Resistance 80 serves to limit the base current of the transistor 81. Transistor 81 is a switching transistor which is normally non-conducting, i.e., when no alarm signal is present in the output of the receiver. Resistance 82 is the collector load resistor for transistor 81. However, when a signal is received having the precise frequency to which the reed 63 is tuned and is of suflicient amplitude to cause the reed to vibrate, a voltage is then applied to the base of the transistor 81. This voltage is established almost instantaneously across the condenser 65a in network 65 and when the signal is removed, the D.C. voltage on condenser 65a in circuit 65 collapses almost instantaneously. When a DC. voltage is present across the condenser 65a, the transistor 81 is switched from non-conducting to a conducting condition. Resist ance 85 and the diode 84 serve to maintain a bias voltage for the transistor 83. This causes the transistor 83 to be non-conducting when the transistor 81 is conducting. The series resistors 88 and 89 comprise the collector load resistance for transistor 83.

When no signal of frequency to which the reed 63 is tuned is present, the transistor 81 is cut off, permitting current to flow through resistance 82 and the base-emitter junction of transistor 83. This places transistor 83 in a highly conducting or saturated state. When transistor 83 is saturated, the low resistance represented thereby and by the diode 84 permits the condenser 87 to charge rapidly to the full voltage drop across the resistances 88 and 89. However, when the tone to which the reed 63 is tuned is present, the transistor 81 becomes saturated. This immediately cuts oif transistor 83. Upon cutoff in transistor 83, the condenser 87 is allowed to discharge at a relatively slow rate through resistances 88 and 89. Any time that the alarm signal is removed or interrupted, condenser 87 will be recharged almost instantaneously.

Transistors 90 and 93 along with resistances 92, 94, 95, 96, and 97 constitute a direct current ditferential amplifier which is responsive to the voltage across condenser 87. The setting of the resistance 95 determines the point along the RC discharge characteristic of the condenser 87 at which the transistor 98 will be switched from a normally non-conducting state to a conducting state.

To illustrate alarm use of the system, note that Conclrad transmission of a general alarm signal is at a broadcast frequency in the fomn' of a 1000 cycle tone maintained for 15 seconds. The resistance is set such that the transistor 98 will begin to conduct after a preset delay, preferably of the order of about ten seconds. This time delay may be set from two seconds up to as much as thirty seconds by selection of the time constant of circuits 87, 88, 89.

Transistor 98 serves to operate the relay coil 99. The relay coil 99 when energized moves armature 99a from contact 99b to contact 99c, completing a circuit to a buzzer 101 from battery 30. The relay coil 99 is thereafter maintained energized by flow of current through resistance 100, holding the relay closed so that the buzzer 101 will continue to operate after the trigger signal is removed. Once the contacts of relay 99 have been actuated, the buzzer 101 will continue to operate until a power connection is interrupted.

Thus, with the receiver in an alarm stand-by condition, the reception of a 1000 tone signal will energize the buzzer 101 only if the 1000 cycle signal is maintained for the preset period of the circuit 87, 88, 89. Once the buzzer is energized, a listener will be immediately warned that an alert is in effect. Momentary opening of switch 28 will remove the power from the alarm circuit stopping the buzzer. Switch 19 may then be actuated to change the receiver circuit from its alarm-stand-by to'its normal reception state wherein the audio circuit of the receiver is connected by way of the volume control 17a to the detector circuit, and the speaker 25 is connected to the output of the amplifier 22.

It will be noted that terminal 104 of the buzzer 101 is connected by way of resistance 105 to the alarm terminal 106 of the switch section 190. When the switch 19 is in the alarm position, the energizing signal applied to the buzzer coil 103 is also applied to the speaker 25 so that a distinctive audible signal will be produced by the speaker 25. It will be noted that the speaker 25 is con nected to ground by way of'a phone jack 107. This jack permits the connection to a circuit such as circuit 108 leading to a second speaker 109 so that the system may operate a local speaker and one or more remote speakers.

From the foregoing it will be seen that the RR as well as the audio section of the receiver together with the alarm circuit are powered from battery 30. Battery 30 is maintained in a charged condition by use of the rectifier circuit leading from the power plug 70. The system, by this means is assured of proper operating voltage and may be maintained on a stand-by basis for long periods ready to receive an alarm should any signal corresponding to the frequency of the reed 63 be received. Upon receipt of the signal, the alarm is energized. The receiver may then be switched to a broadcast-receiving condition. It may be maintained in the same physical location with the plug 70 maintaining connection to a power circuit. Alternatively, if the power circuit should be dead or should fail or if it is desired to move the receiver to a different location following reception of an initial alarm, the battery is in a fully charged condition for assuring maximum service as a portable unit at a time of greatest need. Note that triggering of the alarm disconnects the system from the battery 30 except the alarm 101. Battery power thus is required only to power the alarm 101 and the speaker 25 after reception of a keyed signal.

Thus, there is provided a combination which includes a receiver system having a tuned element responsive only to a keyed signal for establishing an alarm. The system may then be switched manually or automatically, as the case may be, to a broadcast-receiving condition. In a preferred embodiment of the invention the switch 19 including sections 19a-19d is manually operable.

In a modification of the invention as shown in FIG- URE 2, the receiver and audio section of the system are mounted in one chassis whereas the alarm and the power supply circuit are mounted in a second chassis which is adapted to be wall mounted in contact with a convenience outlet or otherwise supplied with power for maintaining the battery and the receiver in a charged state. In this embodiment of the invention shown in FIGURE 1, the

switch 19 is automatically actuated by insertion of the chassis into the holder and by removal therefrom. Upon insertion, the circuit from the power supply to the battery is completed as is the circuit from the battery to the alarm circuitry.

More particularly, in FIGURE 2 the receiver portion of the system is housed in a first unit X with the alarm and the power supply system housed in a unit Y (shown dotted). It will be noted that the battery 30 is housed in the unit X but is so connected that it must be charged from unit Y. A multiterminal plug including contacts A-D is provided for connecting the unit X to the unit Y. More particularly, the contacts AA serve to con nect the alarm terminal on the switch section 1% from speaker 25 to the driving coil 150 of a tune reed device. Terminals BB connect the bus 32 in unit X to the bus 32 in unit Y. The terminals CC connect the power supply 151 to the'negative terminal of battery 30. The terminals D-D connect the bus 31 and the negative terminals of battery 30 to the bus 31- in unit Y.

It will be noted that the terminals C and D in unit X are shorted together so that the alarm unit Y will be energized only when connected to the unit X.

The alarm circuit of FIGURE 2 connected to the reed relay 150 may be employed as a separate unit such as illustrated by the unit Y of FIGURE 2 or it may be employed in substitution for the more complex alarm circuit of FIGURE 1. The alarm circuit of FIGURE 2 is preferred in that it is less complex and provides stability that is not present in the alarm circuit of FIGURE 1. More particularly, in accordance with FIGURE 2, the contact 153 associated with the tuning fork 154 is con nected by way of a resistor 155 to the base of a transistor 156. The base is also connected by way of an RC network T to the bus 32'. The emitter electrode of transistor 156 is connected to bus 31'. The collector of transistor 156 is connected to the bus 32' by way of the condenser 157 and variable resistor 158. Elements 157 and 158 form a parallel circuit, the time constant of which determines the switching characteristics of the sensing system. The collector of transistor 156 is connected by way of resistor 160 to the base of a transistor 162. The base of transistor 162 is also connected by wayof resistor 164 and 165 to a parallel circuit including resistor 166 and a thermistor 167 which are connected to the bus 32. The juncture between resistors 164 and 165 is connected by way of resistor 170 to the emitter electrode of transistor 171, by way of resistor 172 to the bus 31' and by way of diode 173 to bus 32'. The emitter electrode of transistor 62 is connected to the bus 32. The collector electrode of transistor 162 is connected to the bus 31 by way of a resistor 175 and to the base of transistor 171. The collector of transistor 171 is connected by way of a relay coil 177 to the bus 31'. It is also connected by way of resistor 178 to the normally open contact associated with relay 177 and to the arm 179 of a second relay 180. The normally closed terminal-associated with relay 180 is connected in series with-the relay coil and thence to the bus 31'. Thearmature of relay 177 is connected by way of conductor 181 to the bus 31.

In operation, when a signal to which the reed 154 is tuned is applied to the terminals A--A and with the buses 31 and 32' energized, the transistor 156 will promptly be rendered non-conductive whereupon the Charge on condenser 157 will begin to leak 011. The time required for the voltage on the base of transistor 162 to become sufiiciently low to permit conduction will be controlled by, the setting of the variable resistor 158. The time constant is somewhat controlled by the parallel circuit including resistors 160, 164, 165, 166 and 167. The thermistor' 167 serves to compensate for variations with temperature of the base-emitter forward conduction knee of the transistor 162. As well-known, the barrier potential of a transistor varies inversely with temperature so that in order to incorporate the desired stability as to the time at which the circuit of FIGURE 2 will actuate the alarm following the onset of the monotonic signal, it was found desirable to provide such compensation.

As transistor 162 begins conduction, transistor 171 also begins to conduct, thereby closing the relay 177. This applies power from bus 32' through the buzzer coil 180. The latter circuit is repeatedly broken by actuation of the armature 179. At the same time the circuit by way of resistor 178 maintains the relay coil 17 7 energized so that the remainder of the circuit may be restored to its standby condition upon termination of the signal on coil 150. The buzzer will then remain energized until manually stopped or otherwise rendered inoperative.

It will be noted that in the foregoing system the systems X and Y are to be mated for stand-by operation. The receiverX may, upon soundingof an alarm, be removed from system Y and then be employed as a conventionally designed portable radio receiver but with the assurance that at the outset the battery 30 is in a fully charged condition. Thus, not only is there provided a reliable stand-by unit, but upon the occurrence of an alarm signaled by the stand-by unit, the receiver unit will then be fully operative for receipt of voice information as may be desired. The system, therefore, is dependent upon power for charging as by way of the power supply 151 only until the time that a major requirement for the use of the alarm-signaling system may come into being.

In FIGURE 3 there is illustrated one embodiment in which the receiver unit X and the alarm system Y are physically encased so that the unit Y will receive the unit X in a manner conveniently adapted for use in its stand-by state. More particularly, a housing 200 is provided with a speaker enclosure 201, a volume control 202 and with an antenna-handle element 203. The unit X may be of a form of a small transistorized radio frequency receiver. In the lower end of the receiver X there is a four terminal plug having terminals corresponding with terminals A-D of unit X, FIGURE 2. A mating plug is provided in unit Y so that the connections AA-DD can be completed by insertion of the unit X into the nest in the unit Y.

Unit Y is provided with male electrical terminals on the rear face thereof for insertion into a convenience outlet such as on the unit 204. The unit Y would be connected with the upper of the two outlet receptacles on the convenience outlet 204 leaving the lower one, the outlet 205, available for normal use. The switches 19a19d of FIGURE l'are actuated by a push bar 206 mounted in the bottom of the nest in the holder Y and adapted to be inserted into a slot in the bottom of the unit X to engage the structure represented by linkage 19 of FIGURE 1. Upon energizing the alarm signaling the receipt of .a keyed tone by the unit Y, the unit X will be lifted from its nest. A spring 19c incorporated in uni-t X and linked as shown in FIGURE 1 will automatically switch'the receiver to the broadcast-receiving condition.

The alarm circuits of FIGURES 1 and 2 are described and specifically claimed in an application of Gerald L. Caprio, filed concurrently herewith, entitled Keyed Alarm System, Serial No. 215,213, filed Aug. 6, 1962.

Having described the invention in connection with certain specific embodiments thereof, it is to be understood that further modifications may now suggest themselves to those skilled in the art and it is intended to cover such modifications as fall within the scope of the appended claims.

What is claimed is:

1.'A radio alarm system comprising R. F.-audio means having supply terminals and operable to produce at an output terminal a signal representative of modulation on a received R.F. carrier, said R.F.-audio means including adjustable gain control means for regulating the signal gain thereof, speaker means selectively connectable to said output terminal, a battery connected to said supply terminals by a first switch means, an alarm unithaving a supply circuit and a signal output terminal and. including normally quiescent alarm generating means, a resonant reed relay tuned to a selected modulation frequency to generate electrical signals responsive thereto and means responsive to persistence of the electrical signals produced by said reed'relay for a time interval of the order of at least several seconds to actuate said alarm generating means to produce a sensible alarm, and multisection switch means having a standby position applying modulation signals from said output terminal to said alarm unit and maximizing signal gain of said R.F.-audio means and having a broadcast position connecting said output terminal to said speaker means and subjecting the signal gain of said R.F.-audio means to said adjustable gain control means.

2. A radio alarm system comprising R.F.-audio means having supply terminals and operable to produce at an output terminal a signal representative of modulation on a received R.F. carrier, said R.F.-audio means including adjustable gain control means for regulating the signal gain thereof, speaker means selectively connectable to said output terminal, a battery connected to said supply terminals by a first switch means, an alarm unit having a supply circuit and a signal output terminal and including normally quiescent alarm generating means, a resonant reed relay tuned to a selected modulation frequency to gener-ate electrical signals responsive thereto and means responsive to persistence of the electrical signals produced by said reed relay for a time interval of the order of at least several seconds to actuate said alarm generating means to produce a sensible alarm, and multisection switch means having a standby position for concurrently applying modulation signals from said output terminal to said alarm unit, completing connection of said supply circuit to said battery and maximizing signal gain of said R.F.-audio means and having a broadcast position for concurrently connecting said output terminal to said speaker means and disconnecting the same from said alarm unit, disconnecting said alarm unit supply circuit from said battery, and subjecting the signal gain of said R.F.- audio means to said adjustable gain control means.

3. A radio alarm system comprising R.F.-audio means having supply terminals and operable to produce at an output terminal a signal representative of modulation on a received R.F. carrier, said R.F.-audio means including adjustable gain control means for regulating the signal gain thereof, speaker means selectively connectable to said output terminal, a battery connected at its terminal to said supply terminals by a first switch means, an alarm unit having a supply circuit and a signal output terminal and including normally quiescent alarm generating means, a resonant reed relay tuned to a selected modulation frequency to generate electrical signals responsive thereto and means responsive to persistence of the electrical signals produced by said reed relay for a time interval of the order of at least several seconds to actuate said alarm generating means to produce a sensible alarm, multisection switch means having a standby position and a broadcast position including a first section for applying signals from said output terminal to said alarm unit input terminal and to said speaker means respectively at said standby and broadcast positions, a second section for connecting and disconnecting said battery with said alarm unit at said respective positions, and a third section for maximizing the signal gain of said R.F.-audio means and subjecting the signal gain to said adjustable gain control means respectively at said standby and broadcast positions, and additional switch means normally connecting said R.F.-audio means to said battery for providing supply voltage therefor and responsive to actuation of said alarm generating means to disconnect said battery from said R.F.-audio means while maintaining the battery connected to said alarm generating means.

4. In a radio alarm system as defined in claim 1, said R.F.-audio means, battery means and speaker means being a self-contained radio receiver housed in a portable casing which is separable from said alarm unit, a housing for said alarm unit adapted to be supported at a stationary location and having a cradle formation conforming to a portion of said radio receiver casing to receive the conforming portion of said casing therein in supported relation on said housing, and interengageable means on said casing and housing for automatically forcing said multisection switch means to said standby position responsive to reception of said casing portion in said cradle formation of said housing.

5. In a radio alarm system as defined in claim 3, said R.-F.-audio means, battery means and speaker means being a self-contained radio receiver housed in a portable casing which is separable from said alarm unit, a housing for said alarm unit adapted to be supported at a stationary location connected to an electrical convenience socket ception of said casing portion .in said cradle formation of said housing.

References Cited by the Examiner UNITED STATES PATENTS 2,744,194 5/ 1956 Auerbach '325-364 2,879,383 3/1959 Powell 325466 2,912,574 11/1959 Gensell 325466 X 3,009,059 11/196=1 Stratton et al. 325364 6,010,098 11/1961 Pomeroy 325364 X OTHER REFERENCES Howard W. Sams Engineering Staff, Serving Transistor Radios, 1st edition, vol. 4, Indianapolis, Howard W. Sams & 00., Inc., 1959, page 92.

DAVID G. REDINBAUGH, Primary Examiner. 

1. A RADIO ALARM SYSTEM COMPRISING R.F.-AUDIO MEANS HAVING SUPPLY TERMINALS AND OPERABLE TO PRODUCE AT AN OUTPUT TERMINAL A SIGNAL REPRESENTATIVE OF MODULATION ON A RECEIVED R.F. CARRIER, SAID R.F.-AUDIO MEANS INCLUDING ADJUSTABLE GAIN CONTROL MEANS FOR REGULATING THE SIGNAL GAIN THEREOF, SPEAKER MEANS SELECTIVELY CONNECTABLE TO SAID OUTPUT TERMINAL, A BATTERY CONNECTED TO SAID SUPPLY TERMINALS BY A FIRST SWITCH MEANS AN ALARM UNIT HAVING A SUPPLY CIRCUIT AND A SIGNAL OUTPUT TERMINAL AND INCLUDING NORMALLY QUIESCENT ALARM GENERATING MEANS, A RESONANT REED RELAY TUNEL TO A SELECTED MODULATION FREQUENCY TO GENERATE ELECTRICAL RESPONSIVE THERETO AND MEANS TO RESPONSIVE TO PERSISTENCE OF THE ELECTRICAL SIGNALS PRODUCED BY SAID REED RELAY FOR A TIME INTERVAL OF THE ORDER OF AT LEAST SEVERAL SECONDS TO ACTUATE SAID ALARM GENERATING MEANS TO PRODUCE A SENSIBLE ALARM, AND MULTIESECTION SWITCH MEANS HAVING A STANDBY POSITION APPLYING MODULATION SIGNALS FROM SAID OUTPUT TERMINAL TO SAID ALARM UNIT AND MAXIMIZING SIGNAL GAIN OF SAID R.F.-AUDIO MEANS AND HAVING A BROADCAST POSITION CONNECTING SAID OUTPUT TERMINAL TO SAID SPEAKER MEANS AND SUBJECTING THE SIGNAL GAIN OF SAID R.F.-AUDIO MEANS TO SAID ADJUSTABLE GAIN CONTROL MEANS. 